The economic importance of composite materials is well known, and there are strong indications that this importance will be increasing into the future. In this regard, and for example, composite materials are being used with increasing frequency in the automotive, naval construction, and aerospace industries. As used herein, the term composite material simply refers to materials made of strong fibers (continuous or noncontinuous) surrounded by a matrix material, wherein the matrix material serves to distribute and secure the fibers and to facilitate transmission of an applied load to the fibers. The fibers and the matrix material used to make composite material parts are generally bonded together by using an appropriately selected molding process.
As way of background, polymer matrix composite material parts have been made in a variety of different molding processes, including, for example, contact molding, compression and depression molding, and resin injection molding. In the context of contact molding, for example, one or more layers of a selected fiber impregnated with resin (generally with an activator or accelerator) are placed on the surface of a mold (male or female). The impregnated resin fibers are then compacted by use of a roller, which also facilitates the removal or squeezing out of any trapped air pockets. The duration of the resin setting stage varies, depending on the amount of activator or accelerator used, from a few minutes to a few hours. Similarly, and in the context of compression molding, a countermold (i.e., one of two molds of a matched two-part mold set) is used to apply pressure uniformly against impregnated resin fibers that have been applied on the surface of the complementary mold. Depression molding is similar to compression molding; however, a vacuum is used to apply pressure against the complementary mold. Finally, resin transfer molding involves injecting an appropriately selected resin mixture into a closed mold containing dry fibers.
Although composite material molding is, in some respects, well known in the art, there has been little advancement with respect to methods for forming hollow composite material components or parts, especially hollow composite material components or parts having complex surface geometries or shapes. Additionally, there has likewise been little development with respect to methods for forming hollow composite material parts that have been structurally or cosmetically enhanced by the addition of selectively positioned core, structural insert, or veneer pieces. For example, U.S. Pat. No. 4,202,856 to Frikken et al. teaches one method for forming a hollow composite material part, but this method is not entirely satisfactory for forming high-precision parts with exacting specifications and tolerances. More specifically, the method taught by U.S. Pat. No. 4,202,856 to Frikken et al. is not entirely satisfactory for forming hollow parts having complex surface geometries because, among other reasons, the disclosed pressure bag (i.e., bladder) does not generally fit snuggly about the underlying mandrel (thereby making it more difficult and less exacting to uniformly apply resin, fibers, and/or core pieces about the mandrel). Moreover, and upon pressurization, the loosely fitting pressure bag poorly and nonconformally forces the uncured composite material into angular recesses of the mold thereby resulting in non-uniformity of material at those sites.
Other methods for forming hollow composite material parts include the methods disclosed in the family of U.S. patents to Nelson et al., namely, U.S. Pat. Nos. 6,458,306, 6,340,509, 6,248,024, and 5,985,197. The methods disclosed in these patents, however, are also not entirely satisfactory for forming hollow parts having complex surface geometries because, among other reasons, the disclosed flexible (but inherently “non-elastic”) thin-film bladders used in these methods also do not fit snuggly about the mandrel (meaning that the disclosed bladders in these methods, without application of vacuum, are similarly nonconformal to the shape of the mandrel). As such, these methods are also not generally amenable for forming hollow composite material parts having one or more selectively positioned core, structural insert, or veneer pieces integrally associated therewith because placement of such pieces about the bladdered mandrel is very inexact. In addition, the flexible but non-elastic thin-film bladders disclosed in these methods also, upon pressurization, poorly and non-uniformly forces the uncured composite material into angular recesses of the mold.
To alleviate these problems, U.S. Pat. No. 6,264,868 to Marchant teaches a method for forming hollow composite material parts, wherein the method utilizes a dual-material mandrel that expands thermally as a solid body such that uncured composite material is pushed uniformly into angular recesses of the mold. In this bladderless method, the dual-material mandrel is made of a water-soluble ceramic body covered by a silicone-elastomer layer that has a coefficient of thermal expansion much greater than the respective coefficients of thermal expansion of the ceramic body and mold. Thus, and upon application of heat, the dual-material mandrel expands uniformly so as to uniformly force the uncured composite material into angular recesses of the mold. U.S. Pat. No. 6,264,868 to Marchant purports that this important feature cannot be achieved accurately by using the balloon or bladder methods known in the art.
Thus, existing state-of-the-art molding systems and related methodologies are not entirely satisfactory for the fabrication of high-precision hollow composite material components or parts, especially those components or parts having complex surface geometries and having one or more core, structural insert, or veneer pieces integrally associated therewith. Moreover, existing molding methodologies have not addressed many of the concomitant problems associated with selectively positioning one or more core pieces on or within the formed hollow composite material components or parts. Accordingly, there is still a need in the art for new and improved molding methodologies and, more specifically, there is a need for a molding methodology that enables the fabrication of a hollow composite material part including those having one or more selectively positioned core, structural insert, or veneer pieces integrally associated therewith. The present invention fulfills these needs and provides for further related advantages.